1. Field
The present invention includes methods, apparatus and systems related to the reduction of undesired warping in polymers with continuous fibers. For example, the present invention improves the quality of polymers strengthened with glass fibers also known as fiber-reinforced-polymers (FRP) composites.
2. Description of the Related Art
Polymers used in any of a number of different manufacturing fields, including automobile manufacturing, may benefit from increased strength and stiffness. FRP composites may have benefits based on selection and usage. And as the materials used to produce the FRP composites are customizable selected, a wide variety of benefits may be achieved, including, being light weight, having high strength-to-weight ratio, directional strength, corrosion resistance, weather resistance, dimensional stability, low thermal conductivity, low coefficient of thermal expansion, radar transparency, non-magnetic, high impact strength, high dielectric strength (insulator), low maintenance, high durability, part consolidation, small-to-large part geometry possibilities and tailored surface finishes.
For example, in the field of automotive manufacturing, stronger polymers or FRPs may provide for a more effective bumper, a longer lasting body panels, sturdier wind-shield wipers, and the like. Indeed, the desire for stronger and/or stiffer polymers is well recognized.
As is currently practiced, two main techniques are employed to generate stronger polymers. The first technique is to add continuous fiber tapes to a heated polymer prior to molding and cooling to result in a FRP composite. However, without more, the resulting FRP composite may be warped, and therefore is not ideal for the fitting of the molded polymer into other parts (when the molded polymer is a component of a larger system), or for products where a flat and strong FRP composite is desirable.
FIG. 1A illustrates a conventional, prior art polymer having a layer of glass fiber tape for strengthening the polymer in a heated stage. While heated, the layer of polymer and the layer of glass fiber of the FRP composite may appear to be substantially flat. However, as the FRP composite cools down, warping begins to take place, as the polymer is unable to cause the glass to shrink to the same size as the polymer. This causes the undesired warping of the FRP composite. The result, as shown in FIG. 1B, is that the polymer layer contracts more than the glass layer, causing significant warping to the FRP composite.
More particularly, the warping results because the coefficient of linear expansion (a) for glass is significantly lower compared to the polymer. For example,αG=5×10−6 mm/mm·c whereas a polymer may have a CLTE of approximately,αP=1×10−4 mm/mm·c. 
One known way of reducing warping is to lay continuous fiber tapes in varying orientations (e.g., 0°, 45° or 90°) within the polymer. However, this approach is very expensive, inconsistent and requires a trial-and-error process.
Alternatively, strengthening a polymer may be done by adding chopped fibers into a melted polymer, thereby mixing the fiber into the polymer and injecting the resulting mixture into a mold.
However, using chopped fibers (e.g., fibers chopped down to 2 mm-5 mm pieces) for increasing the strength of a polymer is not ideal, and suffers from various drawbacks, including a resulting FRP composite that is not as strong.
Therefore, what is needed is a method, apparatus and/or system which accounts for the difference in the coefficient of linear expansion of glass and polymers, such that when glass is added to a polymer, the resulting product does not suffer the effects of significant warping, and provides a resulting polymer that is much stronger.